GE Wellington coffee table, model RC 4842-A

[TC Chris]

Are those legs the screw-in style,or are they integrated with the cabinetry (glued in structural members)?

I like the looks of the louvers, but they certainly are not compatible with accurate sound dispersion. Turning them upward would look odd, so grille cloth is probably your best option.

Chris Campbell

[stbasil]

The legs screw in, should be easy to remove, but you have to remove those masonite bottom panels to get to them. I agree that grille cloth would be better looking, just have to get the right color!

I was happy to find that this cabinet is solidly built, and uses Phillips head screws instead of flat heads. When I was restoring my Motorola SK111, all the cabinet screws were flat heads, much more difficult to work with, especially when using an electric screwdriver! Cabinet makers must have switched over to Phillips sometime in the mid 60's?

[electra225]

All the Magnavox cabinets I have use "minus head" screws in the cabinet. I replaced certain of them as I restored the cabinet because I could get more "squeeze" on a Phillips head screw.

[stbasil]

Whoops, I meant to say flat blade instead of flat head. Not familiar with "minus head" term, but after looking it up, that's the type the Motorola used.

[stbasil]

I've added a line fuse and have been further checking the electronics before I am comfortable wrapping that part of this restoration, but it's pretty frustrating since I don't have an accurate schematic. I've got a couple of similar schema (for portables) but there are some significant component differences in the amp circuits. The PCB has no markings, and all the hardwiring makes manipulation extremely difficult.

Any suggestions on where I can find an accurate schematic, preferably a complete service manual? I have googled and checked all the usual sources, but no luck.

[electra225]

A minus head screw takes a flat blade screwdriver. A plus head screw is commonly called a Phillips screw. Plus head and minus head may be considered colloquial nomenclature, they use it commonly in Missouri. In Benton County Missouri what do you reckon they call that pipe on the end of your driveway, parallel to the road, that lets water pass down the ditch, and not wash out your driveway or allow water to run across the road? Most places call that a culvert. In Benton County Missouri that is called a whistle.

[TC Chris]

I've added a line fuse and have been further checking the electronics before I am comfortable wrapping that part of this restoration, but it's pretty frustrating since I don't have an accurate schematic. I've got a couple of similar schema (for portables) but there are some significant component differences in the amp circuits. The PCB has no markings, and all the hardwiring makes manipulation extremely difficult.

Any suggestions on where I can find an accurate schematic, preferably a complete service manual? I have googled and checked all the usual sources, but no luck.

If you've checked out individual parts, I'd say go ahead and take the jump. Do a dim bulb test and then fire it up completely.

Chris Campbell

[stbasil]

Already have it working, seems to play fairly well, but audio checks with sine waves and scope suggest some issues with channel balance which I'd like to get sorted if possible. At any rate, I would just like to have an accurate schematic for this thing --it's out there somewhere!

Meanwhile, I'm working on the changer cosmetics, after that, I'll start on the cabinet.

[stbasil]

Decided to attempt cosmetic repair of the platter, and if that didn't work, cover it with a generic rubber mat. The original rubber is rock-hard, and has shrunk, creating radial cracks, allowing the light color paint underneath to show through. Maybe was stored in a hot attic for a long time; fortunately the cabinet is still in good shape.

Speaking of heat, I was happy to find that there is a horizontal slot, hidden underneath the lip of the cabinet top on the amp side, which ventilates the electronics, so GE did address that!

After ruminating on various types of materials to fill those cracks, I decided on spackling compound, tinted black. I used an Exacto knife to work the stuff into the cracks, letting it set for a while, then wiping with a damp paper towel to get most of the excess off.

I'm happy enough with the results, it's not like new, but significantly better looking now. Before and after photos:

Before

After

[William]

Wow, that worked out well and it did not cost you much money.

Bill

[stbasil]

With new stylus and cleaning, the changer sounds good, and works perfectly with all record sizes, amazingly enough. It tracks and trips at 2.5 grams for LPs, but needs another gram for 78s.

I'm adding a Bluetooth adapter, using a 2-port audio switch on the phono input, which is the only input available. In doing tests with a signal generator (which has a much lower impedance output than the cartridge) I found that there is considerable bass emphasis through the amp due to that impedance difference.

I read that a ceramic cartridge is modeled by a voltage source in series with a capacitor, so I experimented with capacitors in series with the generator and settled on a 1,000 pf value. Music from the Bluetooth adapter now doesn't have the excessive bass emphasis. And in the process, I also learned how that simple bass control works!

The amp's bass control is merely a 3 meg pot across both inputs to ground. This works with the capacitance of the ceramic cartridge to control the bass by changing the input impedance of the amplifier. This schematic is not correct for my amp, but it's close enough to generally see how the controls work:

With the straight low impedance input from the Bluetooth adapter, the bass control has no effect, but with the added series capacitor the control actually impacts the bass as it is supposed to do! So I modified the audio switch internally to add those two series capacitors for only the Bluetooth input channels. The switch will go next to the changer; photos later since the cabinet is somewhat disassembled right now.

[electra225]

Thanks for all the great information! I have a C-100 cartridge in a VM changer that tracks at 3.5 grams, but the changer isn't happy much lighter than that. I think the factory recommendation is 5 grams, but they will track lots lighter than that. The C-100 is a worthy successor the the old VR cartridges.

[stbasil]

This is a fun learning experience, still wish I had an accurate schematic. The Sam's index skips this model series (RC485x), so I guess that means they don't have a manual for it. Many of the components have different values than the schematic I have or aren't even present. For instance, the negative feedback circuit is different, there's no load resistor on the audio transformer secondary, there's no 1 meg resistor across the phono input, etc. But it works....

Currently working on the cabinet modifications. I got the legs off, turns out that wasn't as easy as I first thought, they were doweled in, got them off without damaging the cabinet, thanks to my plunge saw (amazing tool, only have had it a year, but it has really been handy). I've continued to be impressed with the quality of this cabinet, every joint is solid!

Also have removed all four of the the louvers, added a new 15 foot polarized power cord, eliminating the interlock. I had noticed a slight tingle when touching the chassis (while standing on concrete garage floor), went away when reversing the old plug, so there's some mild leakage somewhere, pretty common.

Next up is fabricating the new legs and speaker panels.

[stbasil]

Correction, that should be GE model series RC-484x. I guess the only source is going to be from one of those fat GE service manual books?

[electra225]

Have you tried looking in Beitmans? They have pretty complete coverage of GE equipment...

[stbasil]

The schematic I have been using came from Beitmans, but thenks to your comment, Electra, I just went back and found another amp schematic in the 1964 edition, page 54, for the models RC1641,2, 1651,2, etc. It appears to agree much more closely with my chassis. So, they probably used this amp in those wall-mount, buffet, tabletop, coffee table, etc styles in the 63-65 timeframe. I was not expecting to find a schematic with such a different model number! It's also available on Radiomuseum if you know to look for the right model; I'll upload that one to the downloads section for posterity.